1. Technical Field
The present invention relates generally to data processing networks, and more particularly to a data processing network in which a multiplicity of host processors are connected to shared resources.
2. Related Art
In many data processing networks, a large number of host processors share resources such as a database or storage subsystem. Typically, each host has a high probability of obtaining immediate access, but immediate access is not guaranteed. The cost of guaranteeing immediate access is usually considered to be much greater than the benefit to the user.
The probability of obtaining immediate access can be increased by using various techniques. A direct but rather costly solution is to provide additional network paths and additional storage resources, such as additional paths to duplicate storage servers for read-only storage volumes. Other techniques, such as dynamic routing and load balancing, attempt to use existing network and storage resources more effectively.
Dynamic routing directs each data access requests along a path that is selected in accordance with the resources that are currently available in order to avoid overload of resources in the network. Load balancing assigns alternative resources to the hosts in order to avoid overload of any one of the alternative resources by receipt of simultaneous access requests from a large number of the hosts. For dynamic routing and load balancing to be particularly effective, however, additional resources are required in order to gather intelligence about the current or expected state of the network, and to control or restrict the path of the data access requests in a fashion that is beneficial. These additional resources tend to introduce cost and complexity into the data network and often reduce performance during usual operating conditions.